Sensor systems are used by aircraft. For example, an aircraft uses an enhanced vision system (EVS) or enhanced flight visions system (EFVS) to provide imagery to an aircraft crew. An EVS uses either a passive or an active sensing system to acquire data used to generate imagery of the runway environment. A conventional passive sensor, such as a forward looking infrared (FLIR) camera or visible light spectrum camera, receives electromagnetic energy from the environment and outputs data that may be used by the system to generate video images from the point of view of the camera. The camera is installed in an appropriate position, such as in the nose of an aircraft, so that the pilot may be presented with an appropriately scaled and positioned video image on the display. However, while passive sensors provide relatively high quality video imagery, the passive sensors are often be unable to identify required visual references in certain low visibility conditions such as heavy fog.
Active sensing systems, such as millimeter wavelength (MMW) radar systems (e.g., 94 GHz), transmit electromagnetic energy into the environment and receive return electromagnetic energy reflected from the environment. The active sensing system is generally installed in an appropriate position, such as in the nose of an aircraft. Active sensing systems are expensive and require space on-board the aircraft that might already be required for other types of equipment. In addition, millimeter wavelength radar systems require expensive radome technology. Additionally, both FLIR cameras and millimeter wavelength radar systems may have limited range in certain low visibility conditions such as heavy fog, rain, or other precipitation.
Thus, there is a need for real time or near real time sensing systems for and methods of providing enhanced vision at longer ranges and in inclement weather. Further, there is a need for real time or near real time sensing systems for and methods of providing enhanced vision imagery that are less expensive and do not require additional space on the aircraft. There is also a need for display systems for and methods of providing images of the external scene using radar data from a weather radar system. There is still a further need for systems for and methods of providing images of the runway environment derived from weather radar data where such images enable operation below certain specified altitudes during instrument approaches. Further still, there is a need for systems and methods that achieve higher resolution imaging using X-band and C-band radar data.